Differentiation of the bacterium Bacillus subtilis from the vegetative form into a dormant endospore has provided a powerful model for the study of fundamental problems in developmental biology. The overall goal is to understand how gene expression is coordinated with the assembly of cellular structures during differentiation. At the onset of sporulation a phosphorelay system controls the timing of early gene expression. As differentiation continues gene expression is coupled to the completion of specific morphological landmarks, and is synchronized between two cells. Additionally, morphogenetic proteins guide, and possibly regulate, the construction of sub-cellular structures. In this proposal we will investigate regulatory mechanisms that operate at each of these stages of development. In the first aim we will examine how two response regulators (Spo0A and PhoP) interact to produce two phenotypically different fractions of a clonal population. In the second aim we examine the role of newly discovered channel that connects two cells (forespore and mother cell) during endospore development, and in the third aim investigate the potential roles of two transcription factors in cell-type specific restriction of RNA polymerase sigma factor activity. In the final aim we examine the role of a GTP/ATP hydrolyzing protein in the assembly of the complex coat protein structure of endospores. Success in any one of these aims would represent substantial new information, and significantly impact our ideas in broad areas of cell biology and intercellular communication.